Liver Structure and Function in Yellowtail Kingfish, Seriola lalandi, in Response to Reduced Fish Meal Diets

Alterations to lipid storage, and the consequent effects on liver structure, need to be considered when replacing wild-derived fish meal (wd-FM) with alternative ingredients in formulated diets for commercially aquacultured species. The replacement of wd-FM is likely to alter the available level of precursors for bile acid production, potentially impacting the absorption of dietary lipids and fat-soluble vitamins. In this 252-day study, Yellowtail Kingfish, Seriola lalandi (2.52 ± 0.25 kg; 546 ± 20 mm [fork length; mean ± standard deviation]) were fed five different diets. A 30% wd-FM diet served as a control. Dietary wd-FM inclusions were reduced to 20% and 10%, replaced with FM by-product meal. In addition, dietary wd-FM levels were reduced to 20% and replaced with poultry meal (PM) or soy protein concentrate (SPC) in two other separate diets. Fat deposition in the liver was similar amongst all treatment groups with bile duct proliferation and periductular fibrosis observed in the livers of fish fed diets with wd-FM replacement with 10% PM or 10% SPC. Fish fed FM by-product meal at 10% and 20% replacement displayed similar liver structures to control fish. Yellowtail Kingfish fed a 30% wd-FM diet may have the FM replaced by up to 66.67% FM by-product, 33.3% PM or 33.3% SPC without any significant impact on total bile acid synthesis, storage and excretion and liver lipid storage. This research expands our ability to deliver cost-effective nutritional solutions in support of Yellowtail Kingfish culture.